1. Field of Invention
The present invention relates to a storage system for storing data in a plurality of disk drives and disk conclusters composing the storage system.
2. Description of Related Art
I/O performance of a main memory of a computer having a semiconductor recording device as its recording medium is greater by 3 to 4 orders of magnitude than I/O performance of a disk subsystem (hereinafter, referred to as “subsystem”) having a magnetic disk as its recording medium. Narrowing differences in performance, i.e., improvement of the I/O performance of the subsystem, has been an attempt for some time.
One way to improve the I/O performance of the subsystem is to include a plurality of disk drives for every subsystem to store data on a plurality of the disk drives. Such system is known as so called “disk array” system.
For example, FIG. 2 shows a conventional technique, in which, a system include: a plurality of channel interface units 11 for transferring data between a host computer 3 and a disk controller 4; a plurality of disk interface units 16 for transferring data between a disk drive 2 and the disk controller 4; and a shared memory unit 20 for storing control information about data on the disk drive 2 and a disk controller 4 (e.g., information about the data transfer control within the disk controller 4 and management information about data to be stored in the disk drive 2). In such system, the shared memory unit 20 within one disk controller 4 is accessible from all channel interface units 11 and disk interface units 16.
In the disk controller 4, an interconnection 30 connects between the channel interface units 11 and disk interface units and the shared memory unit 20.
The channel interface unit 11 has an interface to connect with the host computer 3 and a microprocessor (not shown) for controlling input and output to the host computer 3.
The disk interface unit 16 has an interface to connect with the disk drive 2 and a microprocessor (not shown) for controlling input and output to the disk drive 2. The disk interface unit 16 also performs a RAID function.
With a spread of the Internet and the like, business firms handles more and more data, and at a data center or the like, it becomes necessary to store an amount of data greater than one disk controller can deal with.
In order to deal with such a situation, a plurality of disk controllers 4 are used as shown in FIG. 2, and the interface to the host computer 3 thereof is connected to the host computer 3 via an SAN switch 5.
As the amount of data increases, a number of disk controllers 4 connecting to the SAN switch 5 increase. As a result, management of an entire system including the host computer 3 and the SAN switch 5 (the system is hereinafter referred to as a storage area network (SAN)) becomes more complicated.
The following process deals with the problem. First, an SAN appliance 6 is connected to the SAN switch 5. The SAN appliance 6 performs a directory service of data managed by all the disk controllers 4 connected to the SAN switch 5, so that a plurality of the disk controllers 4 appear to be one storage system with respect to the host computer 3. That is, a storage areas provided by individual disk controller 4 appear as one large storage area, and a required amount thereof is allocated to the host computer 3.
Big businesses such as banks, securities firms, and telecommunication companies tend to reduce costs required for operation, maintenance and management of a computer system and storage system by centralizing computers and storages distributed to different places in a data center or the like.
With such a trend, there is a demand for a large scale/high-end disk controller with a support (connectivity) of a channel interface for connecting with hundreds of host computers as well as a support for recording capacity exceeding hundreds of terabytes.
On the other hand, with expansion of an open market in recent years and spread of the storage area network (SAN) there is an increasing demand for a small-scale (compact) disk controller of rich function and high reliability equivalent to the large-scale/high-end disk controller.
To fulfill the former demand, a plurality of conventional large-scale/high-end disk controllers can be connected to form a super huge storage system.
For the latter demand, a smallest model of a conventional large-scale/high/end disk controller may form a device with a smaller rack used therefore.
Also, by connecting a plurality of the devices in smaller racks may provide a storage system for supporting a mid-sized or huge configuration, which is supported by the conventional disk controller.
As described above, there is an increasing need for a system with a scalability that can support a variety of configuration ranging from small-scaled to an ultra-huge with the same architecture with rich function and high reliability. To meet the need, there is a need for a storage system that can operate as one system by clustering a plurality of disk controllers.
In the conventional technique shown in FIG. 2, a plurality of disk controllers 4 are connected with the host computer 3 through the SAN switch 5, whereby the SAN appliance 6 makes the plurality of the disk controller 4 look as one storage system with respect to the host computer 3.
However, a software run on the SAN appliance 6 operates the plurality of the disk controllers 4 as one system, whereby reliability and availability gets lowered compared to a conventional single large-scale disk controller.
Moreover, the disk controller 4 with data requested from the host computer 3 is searched on the SAN appliance 6, whereby its performance is deteriorated.
An object of the present invention is to provide a storage system of a configuration with a scalability that can deal with configurations of wide range of sizes from small-scaled to ultra-huge scale with the same architecture of rich function and high reliability.
Specifically, the object of the present invention is to provide a high-performance and high reliability system used for a storage system using a plurality of disk controllers as single system.